As is well known in the art, the study of movement of a subject is often an essential component of basic research performed in many different scientific fields of endeavor. In order to obtain usable information about the motion of a moving subject, the prior art has provided various photographic techniques that may be grouped under the following headings: photography, stroboscopic photography, light-streak photography, video, fast video and camera-computer systems developed to analyse motion. An example of a prior art apparatus that is used in such photographic techniques appears in Rahikainen, A., Hakkinen, K.; Eras liikkeen valokuvausmenetelma ja sen hyvaksikaytto liikkumisturvallisuuden tutkimisessa. Tyo ja ihminen 1(1987) 2, 104-114.
The two most common photographic techniques that are used for motion studies are light-streak photography and stroboscopic photography. In light-streak photography, miniature spotlights are attached to the moving subject at points of interest that are to be studied in detail. Each of the spotlights generates a beam of light having a selected wavelength. Background lighting is also provided for the subject. The background lighting has another selected wavelength. A filter, mounted in front of the camera allows the transmission of the light produced by the spotlights and prevents the transmission of the light produced by the background lighting reflecting from the subject and the background. A high intensity flash unit produces light that penetrates the filter to produce an image of the subject. Thus, in the photograph produced by the camera, an image of the subject is recorded together with an image of the path of the spotlights, referred to in the art as light-streaks. In stroboscopic photography, the moving subject is seen as a sequence of pictures in a single photograph. Stroboscopic photographs are produced by either lighting the subject by a flashing light of a stroboscopic lamp or by photographing the subject by a camera that has a rotating slit disc that acts as a shutter. Very similar photographs are obtained with either method of stroboscopic photography. However, the slit disc method of stroboscopic photography is more versatile than the stroboscopic lamp method in that photographs may be produced both in sunlight as well as with artificial light. In stroboscopic photography that utilizes a stroboscopic lamp, photographs may only be produced in a darkened environment so that the subject is illuminated by only the flashing stroboscopic lamp.
Light-streak photography and stroboscopic photography produce different kinds of information about the movement of the subject. Light-streak photography marks the path of movement of a moving point of the subject with a miniature spotlight and stroboscopic photography illustrates different phases of the movement as a sequence of pictures. In more specific terms, the light-streaks produced by the spotlights enable one to obtain the path and the velocity of a particular moving point of interest. The sequence of pictures obtained by stroboscopic photography enables one to identify the movements. As can be appreciated, if these two photographic methods were combined, more information would be available, concerning the movement of the subject, than could be obtained by either of the methods standing alone.
The present invention proposes to accomplish the aforesaid by providing an apparatus for producing a photograph containing a stroboscopic sequence of images of the subject together with a series of light-streak images produced by miniature spotlights attached to the subject at the specific moving points of interest. Since both images appear in a single photograph, the different phases of the movement of the subject may be correlated with the light-streaks. This is accomplished in the present invention by an apparatus that includes a rotating disc having a set of filtered apertures and one or more transparent apertures. The filtered apertures are separated from one another and from the transparent apertures by opaque regions of the disc. As the disc rotates in front of a camera and the subject moves between a reflective, darkened backdrop and the apparatus, the light produced by miniature spotlights, attached to the subject, passes through the filter apertures to form light-streak images on a photograph produced by the camera. Background lighting is provided that reflects off the subject and passes through the transparent apertures to produce stroboscopic images of the subject that illustrate the different phases of the motion of the subject.
The advantages of the present invention are manifest. The central advantage of the present invention is that the method and apparatus produces a photograph illustrating a general picture of the motion of the subject. Moreover, different phases and paths of the movement, contained in the motion of the subject, are obtained in a form in which the mathematical and physical nature of the motion may be perceived. Since the light streak and stroboscopic effects are combined and may be viewed in the single photograph, a new and completely different representation of the motion of the subject is obtained over conventional photographic methods.
A further advantage is that the photographic apparatus of the present invention can be used in both natural lighting and in artificial lighting without modification of the apparatus. In this regard, as will become apparent, the apparatus of the present invention may also be inexpensively and simply constructed.
As an ancillary feature of the invention, as will also become apparent, the apparatus and method of the present invention may be easily modified for different applications by appropriate selection of the spotlights, the filters, the reflectivity of the backdrop and the width and spacing of the apertures.